Integrated memory circuits serve as data-storage components in thousands of products, from televisions, to automobiles, to computers. Often, these memory circuits are implemented as arrays of memory cells, with each memory cell storing an electrical charge representative of a one or a zero.
In recent years, these memory cells have been modified to include a layer of ceramic-based ferroelectric material that exhibits electric polarizations, analogous to north-south magnetic polarizations, in response to appropriate electrical signals. One electrical signal polarizes the material to represent a zero, and another signal oppositely polarizes the material to represent a one. The polarizations can be detected with special circuitry that allows recovery of stored data. Memory circuits using these ferroelectric memory transistors generally enjoy advantages, such as faster write cycles and lower power requirements, over conventional charge-storage memories.
More recently, polymer-based ferroelectrics have emerged as a potential substitute for ceramic-based ferroelectrics because they generally overcome or ameliorate problems, such as fatigue and imprint, that ceramic-based ferroelectrics may suffer. Moreover, polymer-based ferroelectrics are generally more amenable to use in multi-layer (stacked) memory circuits, which provide increased storage capacity. However, polymer-based ferroelectrics are not without their own problems.
For example, conventional fabrication methods that deposit the ferroelectric polymer over metal structures separated by empty gaps may create hills and valleys in the deposited ferroelectric material. The changing thickness of the ferroelectric material is undesirable, because it not only causes cell-to-cell performance variations, but also produces too many defective cells and thus reduces manufacturing yield. Poor yield ultimately raises the cost of manufacturing these type memories. Moreover, as the number of layers in a multi-layer memory increases, the hills and valleys tend to become higher and deeper, exaggerating the thickness variations in the deposited ferroelectric material and further detracting from desired performance and yield.
Accordingly, the present inventors have recognized a need for developing other methods of making polymer-based ferroelectric memories.